The present disclosure relates to variable valve systems controlling operations of intake and exhaust valves of engines.
It has been generally known that pump loss can be reduced by advancing the time of closing an intake valve in an intake stroke after a piston top dead center of an engine. Accordingly, more and more variable valve systems, which control the lift-off times, the lift, and the operating angles of intake valves, have been and are being mounted in engines.
For example, in a variable valve system shown in Japanese Patent No. 4108295 (paragraphs [0015]-[0030] and FIG. 1), a control shaft is pivotably supported near a rocker arm, and a swing arm lifting off an intake valve via the rocker arm is pivotably attached to the control shaft. The control shaft includes a protrusion having a tip to which a control arm is pivotably attached. A camshaft rotates such that a rotating cam presses the swing arm via the control arm to lift off the intake valve. When the control shaft and the protrusion rotate at a small angle, the swing start angle of the swing arm changes. Then, with the decreasing lift of the intake valve, the operating angle of the intake valve continuously decreases to gradually advance the end of the lift-off. Even if the lift and the operating angle of the intake valve change, pump loss can be reduced without opening and closing a throttle.